Exposure of cultured cells and animals to cadmium induces the expression of a cadre of defense and repair proteins, as well as proto-oncogenes, intermediate metabolism enzymes and structural proteins. The mechanism by which cadmium affects the expression of most of these genes remains unknown. Cadmium has been shown to affect signal transduction pathways regulated by protein kinase A, protein kinase C and calmodulin. We propose that cadmium influences these pathways to affect the transcription of multiple genes and that the activation of these pathways may be a cause of cadmium-induced diseases, apoptosis, and cancer. We will investigate the hypothesis that cadmium induces gene transcription due to its ability to activate signal transduction cascades in the nematode Caenorhabditis elegans. The goals of this research are to (a) isolate C. elegans genes whose transpiration is induced both by cadmium and agents that modulate signal transduction cascades (e.g., calcium, phorbol esters, cAMP) and then characterize the cellular patterns of expression in response to these agents; (b) identify upstream regulatory elements (UREs) in the promoters of these genes that mediate cadmium-inducibility and cell-specific patterns of transcription; (c) determine if the cadmium-responsive UREs also mediate transcription via signal transduction cascades; and (d) identify homologues of C. elegans cadmium-responsive mRNAs in a human liver-derived cell line, and determine if their expression is regulated via metals and second messengers. Identification of genes whose transcription is affected by both cadmium and second messengers would suggest that the metal is acting via a signal transduction pathway. Common patterns of cell- and developmental stage-specific expression following exposure to cadmium and second messengers would further indicate common pathways of regulation. Finally, the identification of a single URE that confers both metal and second messenger responsiveness would confirm that cadmium is functioning through a signal transduction cascade. We feel that the information derived from the proposed C. elegans studies will be applicable to understanding how cadmium influences human health because of the evolutionarily conserved nature of signal transduction pathways and regulatory mechanisms controlling gene transcription.
